A light valve or multiple light valves are used when a large number of light spots have to be individually modulated.
Prior art deformable mirror light valves can be generally divided into three types:
a. Cantilever or hinged mirror type deflecting the light when bending or tilting. The best known example in this category is the DMD technology developed by Texas Instruments. PA1 b. Membrane light valves where a flat membrane is deformed into a spherical mirror, focusing the light. PA1 c. Grating light valves diffracting the light by forming a periodic pattern. The best known example in this category is the Grating Light Valve being developed by Silicon Light Machines (Sunnyvale, Cal.). Introduction to grating light valves was available at the time of filing this application at the web site of Silicon Light Machines, www.siliconlight.com. That site contained an article entitled "The Grating Light Valve: Revolutionizing Display Technology" by D. M. Bloom of Silicon Light Machines. This type is also referred to as "cyclic recording systems" in earlier literature.
The major disadvantage of the first type, that is, the hinged or cantilevered mirror type, is slow response time. Typically response time in these devices is on the order of 10 microseconds. This is due to the low natural frequency of a cantilever mirror and the large deflection required.
The major disadvantage of the second type, the membrane light valve is difficulty in fabrication, as the membrane is supported around its complete periphery making it difficult to fabricate the cavity under it by micromachining. Micromachining is the most desirable fabrication method for deformable mirror light valves as it uses standard processes which have been developed for the manufacturing of integrated circuits. The difficulty in fabricating a monolithic membrane device of this type requires a multi-step process where micromachining and bonding of a membrane is required. An example of such a membrane device is shown in U.S. Pat. No. 4,441,791. The device cannot be fabricated as a monolithic device (i.e. out of a single piece of silicon) because of the membrane.
The major disadvantage of the third type, that being the grating light valve, is low optical efficiency. In a grating light valve there are two ways to use the device: the zero order beam or the first order. For zero order use, the contrast ratio is poor. For first order use the optical efficiency is low, as each first order beam contains less than 50% of the energy. This can be improved by a method known as "blazing" in which the ribbons in a grating light valve are tilted or by deflecting the multiple ribbons forming a spot using a progressively increasing deflection (i.e. the ribbons forming one spot from a "staircase" shape when deflected). While this can overcome some of the light loss it still requires multiple ribbons for each light spot.
Another object it is the object of this invention to have a device with the fast response time of a grating light valve but with the simplicity and ease of fabrication of simpler devices, having only one moving element per spot. Another object of the invention is to create a light valve with high contrast, high efficiency and ability to handle high incident power. While the main use of the invention is as a linear light valve, a two dimensional array can also be built using the invention.